Impact of the material on the thermal behaviour of heat exchangers-reactors

In the field of Process Intensification, manufacturers offer many technologies of heat exchanger-reactors which differ in the design, the nature of the material and the range of operating conditions. Such systems combine continuous operation with strongly coupled features of heat transfer, hydrodynamics, mixing, mass transfer and reaction that makes the choice of the optimal solution a difficult one. The present paper offers a comparison and a characterisation of heat exchanger-reactors manufactured in different materials: stainless steel and silicon carbide for the process plates, aluminium, stainless steel and silicon carbide for the utility plates. The results underline the advantages and drawbacks of each material and the associated impact on the control of industrial applications and, in particular, on the safety aspects.

► The description of five heat exchangers-reactors built in different materials: the process plates could be made of plexiglas, stainless steel or silicon carbide. Different materials could be also used for the utility plates: stainless steel, aluminium or silicon carbide.
► The influence of material on pressure drop: with regards to pressure drop, the choice of material is of little influence. The study also suggests that manufacturing procedures adopted to finish surfaces are more of greater influence than the nature of the material. In view of the wide variety of these procedures (depending on the material and equipment supplier), it appears to draw difficult any conclusions regarding the influence of the material itself.
► The influence of material on heat transfer (heat transfer performances, thermal capacitance): the hybrid reactors appear to be the most interesting ones, as they offer a good compromise that allows both enhanced temperature control and improved safety. Specifically, the use of silicon carbide for process plates and aluminium for utility plates represents the best solution which in addition makes for easier handling in view of the system's limited weight.
► A case study: in spite of the high exothermy (the adiabatic temperature rise is about 100 °C) and the fast kinetics (about 98% of conversion achieved in less than 5 s), the heat transfer performances provide a quasi-isothermal behaviour.